DE2705831A1 - OPTICAL LOCATION DEVICE - Google Patents

Description

PATENT LAWYERS

H NZ-JOACHIM i UÖER

REIN »: R PRIi: TSCH

MONKS 21

GOTTIIAROSTR. 81

Thomson-CSF, Bl. Haussmann 173, 75008 Paris (France)

"Optical Locating Device"

Priority: February 13, 1976, France, No 76 04078

The invention relates to an optical training device, in particular for detecting light sources with a known luminous spectrum, with an optical receiver which contains a tunable optical filter of high selectivity, the transmission frequency of which is time-dependently tunable by a control unit within a predetermined frequency band in order to filter out the different received wavelengths one after the other, with an optoelectronic detection device for the filtered radiation and a processing circuit for the detected signals to separate a useful signal.

The detection device consists of an optical receiver, the is coupled to a photoelectric detector in order to detect the radiation coming from an observation field. The observation field has a certain opening angle and the optical one

The axis of the detection device lies in the middle of the observation field. The received radiation consists of the useful radiation, the comes from the source when it is in the observation field and from interference radiation that comes from external sources of interference and enters the detection device either directly or by reflection. Measured against its true size, the source to be detected is generally very small in the field of observation shining surface. In addition, the radiation emitted by

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the source In die Nachwelselnrlchturif, reached, little opposite the interference radiation from the entire observation area. The interference radiation In general, consists of the sunlight that very much can be intense.

This is how the radiation comes in for a given direction of observation of the stray light from the entire solid angle, which is interesting for optical observation. The interfering radiation generates after her Detection of an interfering signal, i.e. a significant amount of noise, while the noise signal comes from a very weak radiation source and moreover only includes a very small solid angle.

The proof of a signal lying above the noise is possible, but only with very bright sources, which must be very bright, especially if they are far away are.

In order to overcome these difficulties, certain techniques have become known which allow the signal-to-noise ratio to enlarge. We shall briefly remind you of these in the following.

One possible solution is to provide optical filtering and only a very narrowly limited bandwidth that can be used with matches the source to be detected. Such devices are mainly used to detect monochromatic or off suitable for several monochromatic lines of existing radiation. In this way, a large part of the interfering radiation is caused by optical Filtering is eliminated and does not enter the detector.

Another possible solution that also works together with the aforementioned can be carried out is a spatial scanning with the help of transparent, on an opaque Carry out underground arranged columns that move transversely to the optical axis of the detection device and a temporal Generate modulation of the signal.

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The invention is based on the object of a locating device for radiation sources to be developed that are characterized by a special high sicnal / noise ratio.

The solution to this problem is described in claim 1.

The exercise device for a light source of known spectral properties consists according to the invention of the following elements: an optical receiver with focusing optics for the light coming from the EeoLachtungsfeld, an optoelectronic Detection device, an optical filter whose passband is suitable for the spectrum in question, this Filter is tunable and of great selectivity and is tuned by a control unit periodically to the in question to investigate the coming spectral range, whereby the different wavelengths are filtered out with each investigation. the The optoelectronic detection device consists of an electronic high-pass filter with a cut-off frequency that is suitable to remove the DC component that results from the interference radiation from the environment.

Further details and advantages of the invention are shown in the following exemplary embodiments with the aid of the schematically simplified Figure drawings explained: it shows

Fig.l various spectral diagrams and their analysis according to the invention;

2 shows a block diagram of a simplified locating device;

3 shows a block diagram of another locating device;

Fig. 4 to 6 block diagrams of individual elements of the Positioning device shown in Figure 3;

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Flg.7 a compound simplified

Block diagram of an exercise device according to Fig. 3

In Fig. La the spectral composition of the light received by the locating device is within a range of the wavelengths ^ l and Λ 3 limited bandwidth shown. The strength of the interfering radiation, which can generally be attributed to sunlight is, changes very little with wavelength, as its spectrum corresponds to that of blackbody radiation. The spectral intensity changes only slightly as a function of the wavelength and essentially corresponds to an average value LF, which is essentially constant in the frequency band under consideration. The radiation of the light source LS, however, has a spectral structure. In the example chosen, a monochromatic emission with the wavelength /,? accepted.

The principle of the analysis consists in examining the given spectral range from /, 1 to Ä3. This spectral range is sufficiently wide to contain the emission spectra we are looking for. The investigation consists in sliding a spectral window with the center teiAo and a half-value swidth4A over the spectral range to be investigated. In this way, the various components of the radiation, the wavelengths of which are between the values A1 and A3, are examined one after the other by filtering. In the case of a monochromatic emission, the registered signal SD (Fig.Ib) consists of a constant background SC, which is due to the interference radiation produced during the scanning process between times ti to t3, and a useful component SU, which is generated at time t2 became. At time t2 the window of the spectral registration was at wavelength A ²

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According to an advantageous embodiment, the spectral scanning takes place between the wavelengths /, 1 and / \ 2 in a somewhat linear manner, which is illustrated by the sawtooth curves of Plg.lc.

In addition, the spectral scanning process is repeated periodically, preferably with a period T which corresponds to the duration of one pass (Fig.lc). The useful signal SU is repeated with the same frequency (Fig.lb), which finally enables the electronic filtering and almost complete removal of the DC component SC due to the interference radiation .

In Fig.ld the spectrum of an emission source is shown with several discrete spectral lines, as it is generated, for example, by one or more lasers. Whenever the transmission wavelength of the spectral window coincides with the wavelength of one of the emission lines , a signal is generated whose strength corresponds to the intensity of this spectral line. An incoherent radiation source such as an electroluminescent diode can produce a continuous spectrum (FIG. 1e). The examined frequency band from the wavelength Λ 1 to the wavelength A is on the one hand sufficiently narrowed and on the other hand the emission spectrum is covered by this frequency band.

Flg.2 shows a block diagram of a Ortungsvor device according to the invention for the case of a monochromatic emission source. The emission source is illustrated by block 1 and can consist of a laser or a semiconductor laser. The source, which is represented by block 2 , is located some distance from it in the observation area. The source to be detected is a target , generally a missile. The target can be active , ie it can emit radiation of certain wavelengths by itself or it can be passive, in which case it is irradiated by a distant radiation source, which can be located on the ground, and part of the radiation energy into the location device reflected. In both

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Cases it is assumed that the source is an isotropic radiation generated, but in particular also radiates in the direction of the locating device.

The optical receiver is represented by an input lens 3 with the optical axis Z. This is followed by a photoelectric detector 4, the sensitive surface of which lies in the image plane and is centered on the optical axis Z. The optical detector preferably consists of a plurality of detector elements in order to enable spatial localization of the target object. It can consist, for example, of a mosaic of detector elements and thus enable the measurement of the altitude and rare angle to the flight object. For the sake of simplicity, it is currently considered to consist of only one element, which in turn is followed by only one detection and reception channel. For the location of very distant targets, the detector is arranged essentially in the focal point of the objective 3. An optical filter 5 is connected in the beam path and is preferably located as close as possible in front of the detector ¹ J, so that it can be made correspondingly small.

The optical filter is tunable and has a high resolution. The frequency of the filter and, consequently, its very Narrow pass bandwidths are shifted in the spectral range under consideration between the wavelengths λ 1 and A 3 by a control device which supplies an electrical signal. That The emission spectrum of the radiation source is examined in this way.

Such a filter can consist of a crystal of lithium nlobate through which acoustic waves are transmitted with the aid of a piezoelectric transducer. The piezoelectric transducer will controlled by an electrical signal. The mode of operation of such a filter is described in the literature, in particular in the article "Acousto-Optic Tunable Filter" by S. E. Harris and R. W. Wallace, published in the "Journal of the Optical Society of

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America "Vol. 59, No 6, June 1969, pp.

The filter unit consists of a crystal 5 and a control unit 6, which on a predetermined sweeter signal Sl the desired Sets the transmission frequency of the crystal filter 5, the transmission frequency of the crystal filter generally being a puncture the amplitude of the control signal Sl is. In order to generate a time-linear, periodic shift of the pass frequency, the control unit 6 recovers a signal S1 of the shown in Fig. Ic Shape. This signal is generated by a Sögezahn voltage generator 7, which in turn is generated by a synchronization unit 8 incoming periodic time signal with period T (Fig. If) is triggered, generated.

The registered signal SD (Fig.Ib) is pre-amplified (pre-amplifier 9) and treated in an electronic filter 10 to reduce the constant caused by the interference radiation or the receiver noise Remove component SC. The filter 10 is a high-pass filter which can consist of an RC element (shown schematically through the capacitor Cl and the resistor Rl). The filter 10 is an amplifier 11 and possibly an amplitude limiter as well A pulse shaper is connected downstream in order to convert the output signal of the filter 10 into a signal S2 suitable for further processing. The pulses S2 are processed further in the device shown as block 12. In the example considered in Fig. 2 it is a cathode ray oscilloscope whose line flip frequency can be controlled by the synchronization unit H and its vertical deflection by the signal to be detected. Such a system enables the detection of an expected light source in an observation field.

In the more general case where the known spectrum of the emission source has several spectral lines (Fig.Id) or a continuous spectrum (Fig.Ic), the detection device differs from that shown in Fig.2 by additional in

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the detection chain between the filter 10 and the amplifier 11 switched on circuits. As shown in FIG. 3, these additional circuits consist of the correlation circuits 20 and 21 or from corresponding filters. The amplified signal SU and a reference signal S3 corresponding to the expected shape of the signal SU is given in order to identify the signal by autocorrelation. The reference signal S3 is generated by a generator 20 which is triggered by a synchronization pulse H. That The reference signal is thus generated periodically, specifically with the same period with which the filter 5 is tuned. The circuit 20 has a programmable memory on external Triggering the reference signal S3, which corresponds to the expected spectrum, is generated.

In the event that the emission spectrum is composed of several individual lines, the circuit 20 can consist of delay lines 23, 2k, 25 (FIG. **). These delay lines generate laterally shifted pulses of different amplitudes, which correspond to the shape of the spectrum to be expected (Fig.Id). The different amplitudes can be achieved by means of corresponding predetermined amplification factors of the respective amplifiers. A corresponding structure can be produced by a delay line with several outputs, which supplies corresponding delay values.

In the case of a continuous emission spectrum (Flg.Ie) The circuit 20 can consist of a programmable memory 26 and a subsequent integration element or low-pass filter 27. Triggered by a synchronization pulse H, the generates Memory 26 a pulse train, the envelope of which corresponds to the shape of the spectrum to be expected.

FIG. 6 relates to an exemplary embodiment of a correlation circuit 21 according to FIG. This correlation circuit consists of a multiplier 30 which receives the correlating signals _g

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and which is connected on the output side to two integration circuits. These contain a filter circuit 31 with a pass bandwidth matched to the video spectrum of the received signals and an integration circuit 32. The matched filter 31 consists of a low-pass filter with a cut-off frequency between 1 / 2T and 1 / T in order to remove the undesired components of the video spectrum from the form ellminate. The signal at the output of the filter 31 is essentially uniform and is integrated in the circuit 32. This contains an RC element with the time constant R2C2, which is determined as a function of the period T of the signal and the required response time of the receiver. The time constant is determined so that the signal at the terminals of the integration capacitor C2 essentially corresponds to the mean value of the signal entering the integration circuit. The output signal of the circuit 31 can also be directly painted a corresponding device 3 · ¹ are visualized. For further utilization options represented by a block 35, the signal from the output of the integration circuit 42 is compared in a circuit 33 with a predetermined threshold value VS. The level of the threshold VS is generally determined so that a certain rate of false alarms is not exceeded.

Locating devices for tracking radiation sources are generally able to specify an altitude and a rare angle to a recognized target and, under certain circumstances, based on these Data to automatically align the optical axis of the device with the target. The light detector consists of several for this purpose Elements. For example, a detector with four quadrants and four receiving channels can be used, in which the height and Infrequent deviation angles SX and SY with respect to a given! (Horizontal X-axis and a vertical Y-axis are calculated. Another technique is to use the incident optical light signal modulleren by periodic interruption by adding a Slotted opaque disk penetrates the light beam to be led.

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An execution example of this kind is described with reference to PIp.7. The light detector consists of several strip-shaped detector elements 4a to 4n which lie parallel to the X direction and are lined up next to one another in the Y direction. The modulation is generated Il ¹ by a track on the disc, the uniformly rotating about an axis parallel to the Z axis. A track is considered which consists of transparent slits 40 on an opaque background. The rotation generates a specific digital coding such as a pseudo-random coding. A drive device 42 controlled by the synchronization unit 8 ensures the uniform rotation of the disk 41. It is necessary that a spectral scanning process takes place during the minimum time available between the end of an interruption of the light beam and the subsequent interruption. In other words, if Lm is the width of the smallest slit and Tm is the time it takes for this slit to traverse the optical axis Z, then the period T of the spectral scanning process must be less than or equal to Tm.

Has the detection device downstream of the light detector η similar channels, of which only one for the sake of simplicity the only one shown. The channel, which is connected downstream of the first detector element, consists of a preamplifier 9a, a Filter 10a, an amplifier 11a and a correlation circuit 21a. A common generator for generating the reference signal S3 supplies the multiplication circuits of the η channels 21a to 21n. Each correlation circuit contains a threshold value comparison circuit (33, FIG. 6). In this way, the detector element on which the image of the target falls provides the mutfta signal for the subsequent evaluation 43. In addition to this spatial determination of the Y-coordinates of the target, the circuit 43 determines the X-position of the target. This happens because the temporary shift of the useful signal compared to a given

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a temporal reference signal is measured. To this end you can the circuits 43a to 43n have filter or correlation circuits connected to the caused by the slots 40 Modulation are adapted to finally determine the vertical and lateral offset for further evaluation. E.g. the adjustment circuits 44 and 45 automatically align the Z-axis of the locator with the target. The Höhenelnstel «· Development of the frame 46 is achieved by rotation about an X axis and the lateral adjustment by rotation about a Y axis. The output signals the adjustment circuits 44 and 45 determine these rotations as a function of the offset values SX and SY of the target.

Because a spectral filtering is repeated periodically, it is possible with a locating device according to the invention that To suppress interference radiation of the environment largely, whereby a better functioning of the locating device is guaranteed. In particular, the device according to the invention is suitable for opto-electronic location systems for determining the angle or the storage coordinates of a luminous target.

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Claims (9)

PATENT LAWYERS DIETRICH LEWINSKY HhN- I-'CHIM HUBER Ell · ' K i »R ι k TSCH MjJ M c H LN 2 1 February 11, 1977 ^T!; · B 1 9297-V / Ni Claims . ' 1., Optical locating device, in particular for the detection of * light sources with a known luminous spectrum, with an optical receiver which contains a tunable optical filter of high selectivity, the transmission frequency of which is time-dependently tunable by a control unit within a predetermined frequency band in order to successively the different received wavelengths to filter out, with an optoelectronic detection device for the filtered radiation and a processing circuit for the detected signals for separating a useful signal, characterized in that the control unit (6, 7, 8) is designed so that the examination of the frequency band, which is essentially the expected Spectrum, takes place periodically and that the processing circuit contains a high-pass filter (10) whose cut-off frequency is chosen so that the DC voltage component originating from the ambient interference is removed and the periodic component towards the source useful signal (SU) to be returned is obtained. 2. Locating device according to claim 1 for detecting a light source, the spectrum of which has several different wavelengths , characterized in that the processing circuit after the high-pass filter has a reference signal generator and a correlation circuit (21) which contains the useful signal and a reference signal corresponding to the expected spectrum (S3) receives and that a synchronization circuit with the Period of investigation equal to periodic clock signal generated to the control unit and the reference signal generator 709842/0645 _ ₂ _ ORIGINAL INSPECTED to synchronize. 3. Locating device according to claim 2, characterized in that the reference signal generator has a plurality of connected in parallel Delay lines (23, 24, 25) containing the Receive clock signal simultaneously. 4. exercise device according to claim 2, characterized in that the reference signal generator has a programmable memory which is controlled by the clock signal and which is followed by an integration circuit (27). 5. Locating device according to one of claims 2 to 4, characterized characterized in that the correlation circuit (21) has the following elements connected in series: a multiplication circuit which receives useful and reference signals, a low-pass filter (31) with a cut-off frequency between 1 / 2T and 1 / T, where T is the period of the filter tuning, an integration circuit (32) to form the mean value of the filtered signal and a comparison circuit (33) with one of the mean value corresponding threshold. 6. Locating device according to claim 1, for the detection of fciner monochromatic light source, characterized in that the processing circuit after the high-pass filter (10) contains an amplifier and a pulse shaper (11) which forwards the useful signal (S2) to an evaluation circuit (12) . 7. locating apparatus according to one of claims 1 to 6, wherein the control unit consists of a control part for the tuning of the filter and a generator for generating the tuning signal, characterized in that the tunable "filter consists of a lithium niobate crystal and a piezoelectric transducer a saw tooth chip from the control unit 709842/0645 -3-ORfQtNAL INSPECTED The result is a periodic investigation that is linear over time of the frequency band. 8. exercise device according to claim 7 for angular location of a target, characterized in that it consists of η detector elements (^ a ... ¹ Jn), which are each connected to a channel of an η channels having evaluation system that one, from an opaque, with Slotted, rotatable disk existing modulation device (4l to * »2) and a Lmpfangseinheit (43) are provided in which by filtering and / or correlation from the signals of the η channels angle coordinates (SY, SX) are calculated, and that the smallest the slit is at least so wide that its dwell time in the optical axis is at least equal to the period of the filter tuning. 9. Application of the optoelectronic location system according to one of the Claims 1 to 8 in a system for the detection of luminous targets. 98A2 / 0C4S